The present invention relates to a process and a device for filling multilayer pressure containers with liquids below -10.degree. C.
Pressure tanks that receive high internal pressures are customarily constructed as spheres or cylinders with plane or arched end pieces and with the manner of construction depending upon the process of manufacture. High pressure containers are cast seamless or forged or welded together from thick steel sheet which is bent and cut out as segments. For multilayer pressure containers, a plurality of relatively thin sheet shells are bent and welded together one over the other in several layers. Each shell must tightly abut the neighboring shells, since otherwise the entirety of the shells would not be uniformly subjected to the pressure load. As compared to other finishing techniques, the multilayer construction has several advantages. The innermost shell affected by the product may be constructed of a material different from that used for the pressure-bearing outer shells. Very strong close-grained structural steel is usually employed for the outer shells. The welding seams in the pressure-bearing layers may be staggered, the effect of the welding seams on the total stability remaining negligible. For the preparation of individual shells, heavy machines are not required as they are for thick sheets. Since thin sheets generally have better physical properties than thick sheets and since the quality control with thin sheets is also simpler than with thick sheets, multilayer pressure containers have very advantageous material properties.
Multilayer pressure containers, however, also have some disadvantages over single layer pressure containers. Particularly, the heat conductivity of a multilayer pressure container is lower than that of a massive wall container. This is also seen in the calculation prescription which limit the allowable computation temperature to -10.degree. C. to +400.degree. C. The upper limit of +400.degree. C. may still be expanded with a suitable temperature control of the product to be filled in the container and a corresponding insulation of the multilayer pressure container, since in this instance, due to the higher temperature of the inside layer, it abuts the next layer with increased surface pressure which results a better heat conduction. It is possible to demonstrate by tests that the heat conduction becomes greater with an increasing surface pressure between the layers.
For products to be filled at temperatures below -10.degree. C., multilayer pressure containers have not been suitable since the inner shell is subjected to a low product temperature and contracts relative to the overlying shell. This leads to a lessening of the surface pressure between the layers. The bearing strength of the outer layers is then no longer guaranteed. Also, with high inner pressure settings, plastic deformation or even failure of the inner shell may occur.